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Laser-produced plasmas are bright, short sources of X-rays often used for time-resolved imaging and spectroscopy. Absolute measurement requires accurate knowledge of laser-to-x-ray conversion efficiencies, spectrum, photon yield and angular distribution. Here we report on soft X-ray emission from a thin Si foil irradiated by a sub-PW picosecond laser pulse. These absolute measurements cover a continuous and broad spectral range that extends from 4.75 to 7.5 Angstroms (1.7-2.6 keV). The X-ray spectrum consists of spectral line transitions from highly charged ions and broadband emission with contributions from recombination, and free-free processes that occur as electrons decelerate in plasma electromagnetic fields. These quantitative measurements are compared to particle-in-cell simulations allowing us to distinguish bremsstrahlung and synchrotron contributions to the free-free emission. We found that experiment and simulation estimations of laser-to-bremsstrahlung conversion efficiency are in a good agreement. This agreement illustrates the accuracy of experiment and physical interpretation of the measurements.

Excess adsorption of cyclohexanone, cyclohexanol and tert-butanol over metal–organic frameworks Cr-MIL-100 and structurally close Cr-MIL-101 from n-hexane was measured at room temperature. Apparent adsorption equilibrium constants were calculated under the assumption of monolayer adsorption. Two types of adsorption centers turned out to be enough to build a model of experimental isotherms for cyclohexanone, cyclohexanol, and tert-butanol. The first type of centers is characterized by a high value of adsorption equilibrium constant, 1 × 103–3 × 103, and the fraction of such centers is ca. 0.2 for cyclohexanone and tert-butanol and ca. 0.4 for cyclohexanol. The second type of centers possesses a relatively low affinity to guest molecules (the adsorption equilibrium constant varies from 1.8 to 9) and occupies the rest of the surface of the adsorbent The centers with a strong affinity to oxygen-containing guests are associated with chromium atoms within MIL framework.

This paper aims at a comparison of the stability and catalytic performance of niobium- and titanium-containing mesoporous silicates prepared by evaporation-induced self-assembly (EISA) in selective oxidations with hydrogen peroxide. The catalysts comprised evenly dispersed dimeric and/or small oligomeric active sites (M Nb(V) or Ti(IV)), and the Nb sites revealed better hydrolytic stability than the Ti ones, as demonstrated by DRS UV–vis. An attempt has been made to rationalize the differences observed in chemo- and regioselectivity of alkene epoxidation using kinetic modeling tools. The rate law established for cyclooctene epoxidation over the Nb- and Ti-catalysts is consistent with an Eley–Rideal mechanism that involves adsorption of H2O2 on M sites, interaction between M and H2O2 to afford a hydroperoxo species ‘MOOH’ and water, followed by oxygen transfer from ‘MOOH’ to C C bond, producing epoxide and regenerating M. The higher epoxidation (heterolytic pathway) selectivity of the Nb catalysts is, at least partially, related to their lower activity in H2O2 unproductive decomposition. The apparent activation energy of H2O2 degradation is higher for Nb-silicate (20.5 vs 14.8 kcal/mol for Ti-silicate), while the activation energies of epoxidation follow an opposite trend (11.9 vs 14.2 kcal/mol). The heterolytic pathway selectivity of Nb catalysts can be greatly improved by decreasing the reaction temperature. The difference in regioselectivity of limonene epoxidation over Nb- and Ti-silicates observed in MeCN, where the nature of the catalysis is truly heterogeneous, indicates different structures of the active ‘NbOOH’ and ‘TiOOH’ species and/or different mechanisms of the oxygen transfer step. The inversion of regioselectivity observed for Nb catalyst in MeOH may be caused by Nb leaching in this solvent and/or changing the structure of ‘NbOOH’.

In the paper, an X-ray spectroscopy-based approach on laser pulse temporal profile characterization is described. The structure of dielectronic satellites to H-like Ly&alpha, lines strongly depends on a plasma electron density, so it can be applied for diagnostics. These spectral lines are mainly emitted during initial stage of laser plasma expansion. It means that plasma parameters obtained via them characterizes matter conditions in a region surrounding a spot of laser-matter interaction. In the case when a laser contrast is high enough, the radiation interacts with cold matter, which had not been preliminary perturbed by a laser prepulse, and the satellites structure shape corresponding to high densities should be observed. It allows us to consider the satellites as a diagnostic tool for the laser temporal profile quality. In the paper dependencies of the dielectronic satellites structure on electron densities obtained from detailed kinetic calculations in the wide range of plasma parameter for different elements are under discussion. Fundamental theoretical aspects of plasma diagnostic based on the feature of satellite structures shape in hot dense plasma, which led to development of the proposed method, are also explained.

Zr-based metal-organic frameworks (Zr-MOF) UiO-66 and UiO-67 catalyze thioether oxidation in nonprotic solvents with unprecedentedly high selectivity toward corresponding sulfones (96-99% at ca. 50% sulfide conversion with only 1 equiv of H2O2). The reaction mechanism has been investigated using test substrates, kinetic, adsorption, isotopic (18O) labeling, and spectroscopic tools. The following facts point out a nucleophilic character of the peroxo species responsible for the superior formation of sulfones: (1) nucleophilic parameter XNu = 0.92 in the oxidation of thianthrene 5-oxide and its decrease upon addition of acid; (2) sulfone to sulfoxide ratio of 24 in the competitive oxidation of methyl phenyl sulfoxide and p-Br-methyl phenyl sulfide; (3) significantly lower initial rates of methyl phenyl sulfide oxidation relative to methyl phenyl sulfoxide (kS/kSO = 0.05); and (4) positive slope ρ = +0.42 of the Hammett plot for competitive oxidation of p-substituted aryl methyl sulfoxides. Nucleophilic activation of H2O2 on Zr-MOF is also manifested by their capability of catalyzing epoxidation of electron-deficient C═C bonds in α,β-unsaturated ketones accompanied by oxidation of acetonitrile solvent. Kinetic modeling on methyl phenyl sulfoxide oxidation coupled with adsorption studies supports a mechanism that involves the interaction of H2O2 with Zr sites with the formation of a nucleophilic oxidizing species and release of water followed by oxygen atom transfer from the nucleophilic oxidant to sulfoxide that competes with water for Zr sites. The nucleophilic peroxo species coexists with an electrophilic one, ZrOOH, capable of oxygen atom transfer to nucleophilic sulfides. The predominance of nucleophilic activation of H2O2 over electrophilic one is, most likely, ensured by the presence of weak basic sites in Zr-MOFs identified by FTIR spectroscopy of adsorbed CDCl3 and quantified by adsorption of isobutyric acid.

We analyze, using experiments and 3D MHD numerical simulations, the dynamics and radiative properties of a plasma ablated by a laser (1 ns, 10$^{12}$-10$^{13}$ W/cm$^2$) from a solid target, as it expands into a homogeneous, strong magnetic field (up to 30 T) transverse to its main expansion axis. We find that as soon as 2 ns after the start of the expansion, the plasma becomes constrained by the magnetic field. As the magnetic field strength is increased, more plasma is confined close to the target and is heated by magnetic compression. We also observe a dense slab that rapidly expands into vacuum after ~ 8 ns; however, this slab contains only ~ 2 % of the total plasma. As a result of the higher density and increased heating of the confined plasma, there is a net enhancement of the total x-ray emissivity induced by the magnetization., 15 pages, 4 figures, Supplementary Information, submitted to PRL

In this work, we optimized a clean, versatile, compact source of soft X-ray radiation $(E_{\text{x}\text{-}\text{ray}}\sim 3~\text{keV})$ with an yield per shot up to $7\times 10^{11}~\text{photons}/\text{shot}$ in a plasma generated by the interaction of high-contrast femtosecond laser pulses of relativistic intensity $(I_{\text{las}}\sim 10^{18}{-}10^{19}~\text{W}/\text{cm}^{2})$ with supersonic argon gas jets. Using high-resolution X-ray spectroscopy approaches, the dependence of main characteristics (temperature, density and ionization composition) and the emission efficiency of the X-ray source on laser pulse parameters and properties of the gas medium was studied. The optimal conditions, when the X-ray photon yield reached a maximum value, have been found when the argon plasma has an electron temperature of $T_{\text{e}}\sim 185~\text{eV}$ , an electron density of $N_{\text{e}}\sim 7\times 10^{20}~\text{cm}^{-3}$ and an average charge of $Z\sim 14$ . In such a plasma, a coefficient of conversion to soft X-ray radiation with energies $E_{\text{x}\text{-}\text{ray}}\sim 3.1\;(\pm 0.2)~\text{keV}$ reaches $8.57\times 10^{-5}$ , and no processes leading to the acceleration of electrons to MeV energies occur. It was found that the efficiency of the X-ray emission of this plasma source is mainly determined by the focusing geometry. We confirmed experimentally that the angular distribution of the X-ray radiation is isotropic, and its intensity linearly depends on the energy of the laser pulse, which was varied in the range of 50–280 mJ. We also found that the yield of X-ray photons can be notably increased by, for example, choosing the optimal laser pulse duration and the inlet pressure of the gas jet.

Niobium-containing mesoporous silicates reveal superior activity and selectivity in epoxidation of alkenes using hydrogen peroxide as a green oxidant and, in contrast to mesoporous titanium silicates, catalyze epoxidation of both electron-rich and electron-deficient C C bonds. This report describes a kinetic and mechanistic investigation of epoxidation of two representative substrates, cyclooctene (CyO) and 2-methyl-1,4-naphthoquinone (MNQ), over two mesoporous niobium silicates with predominantly di(oligo)meric or isolated Nb(V) sites. The observed kinetic regularities did not depend on the state of Nb but were strictly determined by the nature of the organic substrate. The rate law established for CyO is consistent with a mechanism that involves interaction of H2O2 with Nb(V) sites to give a hydroperoxo species NbOOH and water, followed by oxygen transfer to a nucleophilic C C bond, producing an epoxide and regenerating the initial state of the catalyst. This mechanism is strongly supported by stereospecificity in epoxidation of cis-alkenes and high heterolytic pathway selectivity in the oxidation of cyclohexene. The NbOOH species is manifested by an absorption feature at 307 nm in diffuse reflectance UV–vis spectra. The addition of a base (NaOAc) causes a shift of the absorption band to 293 nm and produces a rate-retarding effect on the epoxidation reaction. Several lines of evidence, including zero reaction order in MNQ, rate-accelerating effect of base, detection of acetamide in the reaction mixture, negligible reaction rate in ethyl acetate, and recognition of weak basic sites in the niobium silicates using infrared spectroscopy of adsorbed CDCl3, all indicate that MNQ epoxidation proceeds by another mechanism that involves rate-limiting oxidation of the solvent molecule (MeCN) to generate peroxycarboximidic acid, which reacts with electron-deficient C C bonds, producing an epoxy derivative and acetamide.

The aromatic hydroxylation of pseudocumene (PC) with aqueous hydrogen peroxide catalyzed by the divanadium-substituted γ-Keggin polyoxotungstate TBA4[γ-PW10O38V2(μ-O)(μ-OH)] (TBA-1H, TBA = tetrabutylammonium) has been studied using kinetic modeling and DFT calculations. This reaction features high chemoselectivity and unusual regioselectivity, affording 2,4,5-trimethylphenol (TMP) as the main product. Then the computational study was extended to the analysis of the regioselectivity for other alkoxy- and alkylarene substrates. The protonation/deprotonation of TBA-1H in MeCN/tBuOH (1:1) was investigated by 31P NMR spectroscopy. Forms with different protonation states, [γ-PV2W10O40]5– (1), [γ-HPV2W10O40]4– (1H), and [γ-H2PV2W10O40]3– (1H2), have been identified, and the protonation equilibrium constants were estimated on the basis of the 31P NMR data. DFT calculations were used to investigate the oxygen transfer process from hydroperoxo species, [γ-PW10O38V2(μ-O)(μ-OOH)]4– (2) and [γ-PW10O38V2(μ-OH)(μ-OOH)]3...

Chromium-based metal-organic frameworks MIL-101 and MIL-100 catalyzed oxidation of propylene glycol (PG) using tert-butyl hydroperoxide (TBHP) as oxidant. The main oxidation product was hydroxyacetone (HA) while minor oxidation products were acetaldehyde and acetic acid. The best results (88% selectivity toward HA at ca. 10% PG conversion) were achieved over MIL-101 using acetonitrile as solvent. In water, C C bond cleavage products predominated. MIL-101 and MIL-100 revealed different behavior toward adsorption of PG from MeCN solution, which affected their catalytic performances. Additives of radical chain scavengers produced a strong rate-inhibiting effect whereas the presence of molecular oxygen accelerated the reaction, suggesting radical chain mechanism of the oxidation process. The oxidation of PG over MIL-101 at 50 °C proceeded without leaching of the active metal into solution and the catalysis had the truly heterogeneous nature. The MIL-101 catalyst could be recycled without significant loss of activity and selectivity and preserved its structure during, at least three, catalytic cycles.

In the paper, an X-ray spectroscopy-based approach on laser pulse temporal profile characterization is described. The structure of dielectronic satellites to H-like Lyα lines strongly depends on a plasma electron density, so it can be applied for diagnostics. These spectral lines are mainly emitted during initial stage of laser plasma expansion. It means that plasma parameters obtained via them characterizes matter conditions in a region surrounding a spot of laser-matter interaction. In the case when a laser contrast is high enough, the radiation interacts with cold matter, which had not been preliminary perturbed by a laser prepulse, and the satellites structure shape corresponding to high densities should be observed. It allows us to consider the satellites as a diagnostic tool for the laser temporal profile quality. In the paper dependencies of the dielectronic satellites structure on electron densities obtained from detailed kinetic calculations in the wide range of plasma parameter for different elements are under discussion. Fundamental theoretical aspects of plasma diagnostic based on the feature of satellite structures shape in hot dense plasma, which led to development of the proposed method, are also explained.

Hydrothermally stable mesoporous niobium-silicates Nb-MMM-E have been first prepared following the convenient and versatile evaporation-induced self-assembly (EISA) methodology. The new materials have been characterized by elemental analysis, XRD, low-temperature N2 adsorption, SEM, XPS, DRS UV–vis, and Raman techniques. DR UV–vis spectroscopy enabled differentiation between isolated and oligomerized Nb centers on the silica surface. Use of niobium(V) ethoxide modified with acetylacetone (acac) as a Nb source favored the formation of dimeric and/or small oligomeric Nb centers on the surface of mesoporous silica while ammonium niobate(V) oxalate coupled with acac gave mostly site-isolated Nb species. The Nb-MMM-E materials catalyzed selectively oxidation of various unsaturated compounds of interest for fine and specialty chemistry using the green oxidant – aqueous hydrogen peroxide. Epoxidation of both electron rich and electron deficient CC bonds could be accomplished over Nb-MMM-E. While catalysts with isolated Nb centers were preferable for the selective formation of epoxides sensitive to ring opening and overoxidation, both single site and oligomerized Nb centers were equally effective for the production of relatively stable epoxides. The truly heterogeneous nature of the catalysis over Nb-MMM-E and absence of Nb leaching into solution have been proved by hot filtration tests coupled with elemental analysis. The catalysts could be easily recovered by filtration and reused several times without significant deterioration of the catalytic performance.

We irradiated soft X-ray laser pulses onto aluminum film targets, which were evaporated on silicon and lithium fluoride substrates. After laser irradiation, we observed irradiated surfaces and confirmed damage with nanometer scale-modified structures. These damage structures were the same as those formed on the aluminum bulk surface. In this article, we discuss a possibility of the growth process of damage structures on the Al surface based on the experimental results.

We present new diagnostics for use in optical laser pump - X-ray Free Electron Laser (XFEL) probe experiments to monitor dimensions, intensity profile and focusability of the XFEL beam and to control initial quality and homogeneity of targets to be driven by optical laser pulse. By developing X-ray imaging, based on the use of an LiF crystal detector, we were able to measure the distribution of energy inside a hard X-ray beam with unprecedented high spatial resolution (∼1 μm) and across a field of view larger than some millimetres. This diagnostic can be used in situ, provides a very high dynamic range, has an extremely limited cost, and is relatively easy to be implemented in pump-probe experiments. The proposed methods were successfully applied in pump-probe experiments at the SPring-8 Angstrom Compact free electron LAser (SACLA) XFEL facility and its potential was demonstrated for current and future High Energy Density Science experiments.We present new diagnostics for use in optical laser pump - X-ray Free Electron Laser (XFEL) probe experiments to monitor dimensions, intensity profile and focusability of the XFEL beam and to control initial quality and homogeneity of targets to be driven by optical laser pulse. By developing X-ray imaging, based on the use of an LiF crystal detector, we were able to measure the distribution of energy inside a hard X-ray beam with unprecedented high spatial resolution (∼1 μm) and across a field of view larger than some millimetres. This diagnostic can be used in situ, provides a very high dynamic range, has an extremely limited cost, and is relatively easy to be implemented in pump-probe experiments. The proposed methods were successfully applied in pump-probe experiments at the SPring-8 Angstrom Compact free electron LAser (SACLA) XFEL facility and its potential was demonstrated for current and future High Energy Density Science experiments.

X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5 × 1020 and 2.5 × 1020 W∕cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.

The use of gas cluster media as a target for an intense femtosecond laser pulses is considered to be uniquely convenient approach for the development of a compact versatile pulsed source of ionizing radiation. Also, one may consider cluster media as a nanolab to investigate fundamental issues of intense optical fields interaction with sub-wavelength scale structures. However, conventional diagnostic methods fail to register highly charged ion states from a cluster plasma because of strong recombination in the ambient gas. In the paper we introduce high-resolution X-ray spectroscopy method allowing to study energy spectra of highly charged ions created in the area of most intense laser radiation. The emission of CO2 clusters were analyzed in experiments with 60 fs 780 nm laser pulses of 1018 W/cm2 intensity. Theory and according X-ray spectra modeling allows to reveal the energy spectra and yield of highly charged oxygen ions. It was found that while the laser of fundamental frequency creates commonly expected monotonic ion energy spectrum, frequency doubled laser radiation initiates energy spectra featuring of distinctive quasi-monoenergetic peaks. The later would provide definite advantage in further development of laser-plasma based compact ion accelerators.

Ultrashort laser pulse is a unique nanometallurgical tool which operates at extreme conditions: ultimate strength of material, the smallest spatiotemporal scales, and nonequlibrium crystallization. Approaches to ultimate strength and to highly nonequlibrium crystallization are tightly coupled with the smallness of spatiotemporal scales. Usage of the tool opens new opportunities to create materials with enhanced surface hardness, anticorrosion properties, and diverted optical constants. To use these advantages we have first of all to develop clear and reliable physical model. The paper presents new results concerning interactions of optical or X-ray lasers with metals. It is shown that ultrashort laser pulse melts surface layer, sends shock into bulk, and foams molten metal. Dense dislocation bilayer is created thanks to fast recrystallization (the first sublayer) and plastic transformations behind strong shock (the second sublayer). Plastic shock generated at moderate laser intensities attenuates sharply during its propagation into metal. During this attenuation, a plastic shock regenerates into a powerful elastic shock. This process defines boundary between the second dislocation sublayer and undamaged solid. Mechanical breaking of foam after its strong stretching and fly away of a part of melt together with fast freezing are responsible for appearance of chaotic frozen nanostructures at an irradiated surface.

Experimental studies on the formation of highly charged ions of medium-Z elements using femtosecond laser pulses with different contrast levels were carried out. Multiply charged Fe ions were generated by laser pulses with 35 fs duration and an intensity exceeding 1021 W/cm2. Using high-resolution X-ray spectroscopic methods, bulk electron temperature of the generated plasma has been identified. It is shown that the presence of a laser pre-pulse at a contrast level of 105–106 with respect to the main pulse drastically decreases the degree of Fe ionization. We conclude that an effective source of energetic, multiply charged moderate and high-Z ions based on femtosecond laser–plasma interactions can be created only using laser pulses of ultra-high contrast.

We present an overview of our systematic studies of the surface modifications resulting from the interactions of both single and multiple picosecond soft x-ray laser (SXRL) pulses with materials, such as gold (Au), copper (Cu), aluminum (Al), and lithium fluoride (LiF). We show experimentally the possibility of the precise nanometer size structures (~10–40 nm) formation on their surfaces by ultra-low (~10–30 mJ/cm2 ) fluencies of single picosecond SXRL pulse. Comparison experimental results with the atomistic model of ablation, which was developed for the single SXRL shot interaction with dielectrics and metals, is provided. Theoretical description of surface nanostructures is considered and is shown that such structures are formed after laser illumination in a process of mechanical spallation of ultrathin surface layer of molten metal. Spallation is accompanied by a strong foaming of melt, breaking of foam, and freezing of foam remnants. Those remnants form chaotic nanostructures, which are observed in experiments. Our measurements show that electron temperature of matter under irradiation of SXRL was lower than 1 eV. The model calculation also predicts that the ablation induced by the SXRL can create the significant low electron temperature. Our results demonstrate that tensile stress created in LiF and metals by short SXRL pulse can produce spallative ablation of target even for drastically small fluencies, which open new opportunities for material nano processing.

It was shown (Faenov et al., 2015b) that the energy of femtosecond laser pulses with relativistic intensity approaching to ~1021 W/cm2 is efficiently converted to X-ray radiation and produces exotic states in solid density plasma periphery. We propose and show by one-dimensional two-temperature hydrodynamic modeling, that applying two such unique ultra-bright X-ray sources with intensities above 1017 W/cm2 – allow to generate shock waves with strength of up to some hundreds Mbar, which could give new opportunities for studies of matter in extreme conditions.

DOI: 10.1021/acs.inorgchem.6b00621 URL: http://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.6b00621 Filiació URV: SI A DFT study revealed that the mechanism of alkene epoxidation with hydrogen peroxide catalyzed by Ti-containing polyoxometalates (POMs) depends on the Ti coordination environment: For rigid and hindered Ti centers, the unprecedented ß-oxygen transfer from the titanium hydroperoxo species becomes favored over the ß-oxygen one. Improving the model for catalyst description, the calculations were able to reproduce the Arrhenius activation energy values determined in kinetic studies. Unlike protonation, the possible ion-pairing between POMs and countercations has a minor effect on the electrophlicity of the catalyst and, consequently, on the activity of epoxidation.

Experiments with an ultrahigh-contrast femtosecond laser have yielded a new type of X-ray emission spectra with a complex structure consisting of resonance lines against the quasicontinuous background. Some recent work has shown that such spectra can only be accounted for by considering the radiation emitted by multiply charged hollow (empty K shell) ions in an ultradense plasma. This review discusses the observation of the spectra of hollow ions in an ultradense laser plasma and considers the types of such ions and how they are excited. Considerable opportunities of hollow ion spectra-based diagnostic techniques are emphasized.

International audience; We present experiments dealing with a femtosecond laser-driven cluster-based plasma, where by analyzing the nonlinear phenomenon of satellites of spectral lines of Ar XVII, we revealed the nonlinear phenomenon of the generation of the second harmonic of the laser frequency. For performing this analysis we developed new results in the theory of satellites of spectral lines. From such lineshape analysis we found, in particular, that the efficiency of converting the short (40 fs) intense (3x10 18 W/cm 2) incident laser light into the second harmonic was 2%. This result is in the excellent agreement with the 2-Dimensional Particle-In-Cell (2D PIC) simulation that we also performed. There is also an order of magnitude agreement between the thresholds for the SHG found from the line shape analysis and from the 2D PIC simulations.

Oxidation of 2-methyl-1-naphthol (MNL) with molecular oxygen proceeds efficiently under mild reaction conditions (3 atm O(2), 60-80 °C) in the absence of any catalyst or sensitizer and produces 2-methyl-1,4-naphthoquinone (MNQ, menadione, or vitamin K(3)) with selectivity up to 80% in nonpolar solvents. (1)H NMR and (1)H,(1)H-COSY studies revealed the formation of 2-methyl-4-hydroperoxynaphthalene-1(4H)-one (HP) during the reaction course. Several mechanistic hypotheses, including conventional radical autoxidation, electron transfer mechanisms, photooxygenation, and thermal intersystem crossing (ISC), have been evaluated using spectroscopic, mass-spectrometric, spin-trapping, (18)O(2) labeling, kinetic, and computational techniques. Several facts collectively implicate that ISC contributes significantly into MNL oxidation with O(2) at elevated pressure: (i) the reaction rate is unaffected by light; (ii) C-C-coupling dimers are practically absent; (iii) the reaction is first order in both MNL and O(2); (iv) the observed activation parameters (ΔH(‡) = 8.1 kcal mol(-1) and ΔS(‡) = -50 eu) are similar to those found for the spin-forbidden oxidation of helianthrene with (3)O(2) (Seip, M.; Brauer, H.-D. J. Am. Chem. Soc.1992, 114, 4486); and (v) the external heavy atom effect (2-fold increase of the reaction rate in iodobenzene) points to spin inversion in the rate-limiting step.

Bright source of soft X-ray emission was developed. Soft X-ray radiation was produced by femtosecond laser pulses irradiation of submicron size CO2 clusters. These clusters were produced in custom designed supersonic nozzle from the mixture of the 10% CO2 +90 % He expanding gases. Lithium fluorine based soft X-ray detectors was used for registration of absorption images of ultrathin (nanoscale) foils and biological structures illuminated by the developed source. It was demonstrated that even ifthe foil is essentially transparent for the soft X-ray radiation (like 100 nm thick Zr foil), the image contrast could be significantly increased due to the influence of propagation-based phase-contrast effect when detector is placed at the proper distance behind the sample (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An investigation is made of the role of hollow atoms in the spectra of an ultrashort-pulse-laser-driven Ar cluster target. Experimental measurements are presented from an Ar cluster-gas target using short-pulse lasers with various intensities, durations, and contrasts. Calculations in support of these measurements have been performed using a detailed atomic kinetics model with the ion distributions found from solution of the time-dependent rate equations. The calculations are in good agreement with the measurements and the role of hollow atoms in the resulting complicated spectra is analyzed. It is demonstrated that, although the presence of hollow atoms is estimated to add only around 2% to the total line emission, signatures of hollow atom spectra can be identified in the calculations, which are qualitatively supported by the experimental measurements.

To study the ablation process induced by the soft x-ray laser pulse, we investigated the electron temperature of the ablating material. Focused soft x-ray laser pulses having a wavelength of 13.9 nm and duration of 7 ps were irradiated onto the LiF, Al, and Cu surfaces, and we observed the optical emission from the surfaces by use of an optical camera. On sample surfaces, we could confirm damage structures, but no emission signal in the visible spectral range during ablation could be observed. Then, we estimated the electron temperature in the ablating matter. To consider the radiation from a heated layer, we supposed a black-body radiator as an object. The calculation result was that the electron temperature was estimated to be lower than 1 eV and the process duration was shorter than 1000 ps. The theoretical model calculation suggests the spallative ablation for the interaction between the soft x-ray laser and materials. The driving force for the spallation is an increasing pressure appearing in the heated layer, and the change of the surface is considered to be due to a splash of a molten layer. The model calculation predicts that the soft x-ray laser with the fluence around the ablation threshold can create an electron temperature around 1 eV in a material. The experimental result is in good accordance with the theoretical prediction. Our investigation implies that the spallative ablation occurs in the low electron temperature region of a non-equilibrium state of warm dense matter.

Soft x-ray laser (SXRL) pulses were irradiated to the surfaces of LiF, Al, and Cu plate targets. On all irradiated target surfaces, the ablation and/or surface modification structures caused by the SXRL pulse irradiations were confirmed. However, the optical emission (visible spectral range) from the surfaces during the SXRL pulse irradiations were not observed, in spite of high sensitive registration technique. The theoretical model calculations for the interaction between SXRL pulse and material surfaces has revealed the spallative ablation of target surface with a low electron temperature. Our experimental results is consistent with the theoretical model calculations, qualitatively.

The oxidation of thioethers by the green oxidant aqueous H2 O2 catalysed by the tetratitanium-substituted Polyoxometalate (POM) (Bu4 N)8 [{γ-SiTi2 W10 O36 (OH)2 }2 (μ-O)2 ], as a model catalyst comprising tetrameric titanium centres, was investigated by kinetic modelling and DFT calculations. Several mechanisms of sulfoxidation were evaluated by using methyl phenyl sulfide (PhSMe) as a model substrate in the experiments and dimethyl sulfide in the calculations. The first mechanism assumes that the active hydroperoxo species forms directly through interaction of the Ti2 (μ-OH)2 group in [{γ-SiTi2 W10 O36 (OH)2 }2 (μ-O)2 ](8-) (1 D) with H2 O2 . The second mechanism includes hydrolysis of Ti-O-Ti bonds linking two γ-Keggin units in structure 1 D to produce the monomer [(γ-SiW10 Ti2 O38 H2 )(OH)2 ](4-) (1 M), followed by the formation of an active hydroperoxo species upon interaction of the Ti hydroxo group with H2 O2 . Both kinetic modelling and DFT calculations support the mechanism through the monomeric species that involves the hydrolysis step. According to the DFT studies the activation of H2 O2 by compound 1 M is preferred by 6.5 kcal mol(-1) with respect to anion 1 D due to the more flexible Ti environment of the terminal Ti hydroxo group in 1 M. The calculations also indicate that for the "monomeric" mechanism two pathways are operative: the mono- and the multinuclear pathway. In the mononuclear mechanism, the active group is the terminal TiOH group, whereas in the multinuclear path the active group is the bridging Ti2 (μ-OH) moiety. Moreover, unlike previous studies, the sulfoxidation is preferred through a β-oxygen atom transfer from the Ti hydroperoxo group because the α-oxygen atom transfer leads to an unfavourable seven-fold coordinated Ti environment in the transition state. Finally, we have generalised these results to other Ti-containing POMs: the Ti-monosubstituted α-Keggin ion [α-PTi(OH)W11 O39 ](4-) and the dititanium-substituted sandwich-type ion [Ti2 (OH)2 As2 W19 O67 ](8-) .

X pinch plasmas produced from fine metal wires can reach near solid densities and temperatures of 1 keV or even more. Plasma conditions change on time scales as short as 5–10 ps as determined using an x-ray streak camera viewing a focusing crystal spectrograph or directly viewing the plasma through multiple filters on a single test. As a result, it is possible to determine plasma conditions from spectra with ∼10 ps time resolution. Experiments and theory are now coming together to give a consistent picture of the dynamics and kinetics of these high energy density plasmas with very high temporal and spatial precision. A set of diagnostic techniques used in experiments for spectrally, temporally, and spatially resolved measurements of X pinch plasmas is described. Results of plasma parameter determination from these measurements are presented. X ray backlighting of one x- pinch by another with ∼30 ps x-ray pulses enables the dynamics and kinetics to be correlated in time.

The spatial configuration of the ion source generated under femtosecond laser interaction with clusters is investigated. While intense laser pulses (36 fs, 60 mJ, intensity of 4 × 1017 W/cm2) propagated in CO2 cluster (~0.22 μm in diameter) media, the shape of the obtained plasma ion source was registered for the first time by means of pinhole imaging method. The remarkable decrease in fast ion yield in the vicinity of the assumed best laser focus near the gas cluster jet axis is observed. Such observed anisotropy of the ion source is suggested to originate from the influence of the laser prepulse destroying clusters in advance to the arrival of the main pulse. The assumption is confirmed by optical shadowgraphy images of the plasma channel and is important for further development of an efficient laser-plasma-based fast ion source. Following the observed geometry of the ion source, the laser intensity limit allowing to accelerate ions to ~100 keV energy range was estimated.

CO\(_2\) clusters formed in supersonic expansion of a mixed-gas of CO\(_2\)/H\(_2\) or CO\(_2\)/He through a three-staged conical nozzle have been verified by measuring the angular distribution of the light scattered from cluster target. The angular distribution is fitted by convolving a lognormal size distribution with the scattering coefficients calculated based on the Mie theory. The reliability of the size measurement is verified to be within an experimental error of 10 % using standard particles. The mean sizes of CO\(_2\) clusters at the target center for the cases of CO\(_2\)/H\(_2\) and CO\(_2\)/He gas mixtures are estimated to be 0.26 and 0.22 \(\upmu \)m, respectively. For the CO\(_2\)/H\(_2\) mixed-gas target, the variation of the mean cluster size inside the gas jet is constant within the experimental error. Furthermore, the cluster density is estimated to be \(5.5 \times 10^8\) clusters/cm\(^2\) by measuring the attenuation of the laser beam intensity. In addition, total gas density profiles in radial direction are obtained via the Abel inversion from the phase shift of the light passing through the target by utilizing an interferometer. The variation of the cluster mass fraction along the radial direction of the target is almost constant, which is consistent with a Boldarev’s model.

SSCI-VIDE+CDFA+ISK:IVA:ASO; International audience; Catalytic properties of Fe- and Cr-based metal-organic frameworks (MOFs) MIL-100 and MIL-101 have been assessed in two liquid-phase reactions: solvent-free allylic oxidation of alkenes (cyclohexene, alpha- and beta-pinenes) with molecular oxygen and oxidation of anthracene (AN) with tert-butyl hydroperoxide(TBHP). In the oxidation of alkenes, the product selectivity strongly depends on the nature of metal (Fe or Cr) but, for the same metal, only slightly differs for the MIL-100 and MIL-101 structures. The Fe- containing MOFs afford the formation of unsaturated alcohols while Cr-based MOFs give mainly unsaturated ketones. Both Cr-MIL-100 and Cr-MIL-101 favor decomposition of cyclohexenyl hydroperoxide to produce 2-cyclohexen-1-one with 67-69% selectivity. Stability toward destruction reduced in the order Cr-MIL-101, Cr-MIL-100 > Fe-MIL-100 > Fe-MIL-101. In the oxidation of anthracene over both Cr-MOFs and Fe-MIL-101, the selectivity toward 9,10-anthraquinone (AQ) attained 100% at 92-100% AN conversion. The turnover frequency (TOF) decreased in the order Cr-MIL-101 > Fe-MIL-101 > Cr-MIL-100 > Fe-MIL-100. Cr-MIL-101 revealed superior catalytic performance in terms of AN conversion, AQ selectivity and TOF. Nearly quantitative yield of AQ was obtained after 1.5 h at 100 degrees C in chlorobenzene as solvent. No leaching of active metal occurred under optimal reaction conditions and the MOFs could be recycled several times without deterioration of the catalytic properties. (C) 2014 Elsevier B.V. All rights reserved.

We show experimentally the possibility of the precise nanometer size surface structuring of metal surfaces induced by ultra low fluencies of picosecond soft x-ray laser single pulse. After irradiation processes, we observed the modified surfaces to understand the interactions between the soft x-ray laser pulses and various materials by a scanning electron microscope. The formations of unique modified structures caused by irradiations of the soft x-ray laser pulses were seen. On Al surface, the formations of conical structures were observed. It was found that on Au surface, the ripple-like structures were formed. The atomistic model of ablation is developed that reveals the ultra-low threshold fluence values of this process. Calculated ablation depth as a function of fluence is in good agreement with the experimental data.

A plasma of argon produced with a plasma focus discharge has been observed between 3.8 and 4.2 A. Spectra registered with a spectral resolution of 0.03 A/mm show satellite lines of Ar which were measured and compared with two independent theoretical calculations. Seven transitions of Li-like, eleven of Be-like. twelve of B-like, twenty of C-like, nine of N-like, seven of O-like and two of F-like argon have been identified. The agreement between the observations and the calculations and also between the two sets of calculations is generally good.

We present an analysis of the spectrum of satellite transitions to the He-{beta} line in ArXVII. High-resolution measurements of the spectra from laser-heated Ar-gas-puff targets are made with spectral resolution of 10000 and spatial resolution of better than 50 {mu}m. These are compared with tokamak measurements. Several different lines are identified in the spectra and the spectral analysis is used to determine the plasma parameters in the gas-puff laser-produced plasma. The data complement those from tokamak measurements to provide more complete information on the satellite spectra. {copyright} {ital 1997} {ital The American Physical Society}

To study the interactions between a soft x-ray laser (SXRL) and various materials, we irradiated Al, Au, Cu, and Si with the SXRL beam pulses having a wavelength of 13.9 nm and duration of 7 ps. Following the irradiation, the induced structures were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, conical structures were observed on the Al surface, and ripple-like structures were formed on the Au and Cu surfaces. The conical structures were destroyed under multiple SXRL pulse irradiation. On the other hand, the developments of modified structures were observed after multiple pulse irradiations on the Au and Cu surfaces. On the Si surface, deep holes, that seemed to be molten structures induced by the accumulation of multiple pulse irradiations, were found. Therefore, it is concluded that the SXRL pulse irradiations of various material surfaces cause different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties of each materials, such as the melting point and the attenuation length of x-rays.

A dense jet of a plasma consisting of multiply charged ions was generated in the interaction of a laser plasma with a strong external axial magnetic field. It is shown that using the high-luminosity x-ray spectroheliograph technique allows to measure plasma emission spectra with 2-dimensional spatial resolution even in the cases when these spectra have small intensities. The x-ray spectroscopy and interferometry methods are used to measure plasma parameter distributions. The dependencies of Ne(z) and Te(z) measured in this paper can be used to calculate the evolution of plasma ionization state during plasma expansion. The quasihomogeneous laser jet, which appears when a laser plasma interacts with an external magnetic field can be used not only to form an active medium of a short wavelength laser, but probably also to tackle the urgent problem of transport in a laser ion injector.

We observed that increasing the clusters size and laser pulse contrast can enhance the X-ray flux emitted by femtosecond-laser-driven-cluster plasma. By focusing a high contrast laser (10(-10)) on large argon clusters, high flux Kα-like X-rays (around 2.96 keV) is generated with a total flux of 2.5 × 10(11) photons/J in 4π and a conversion efficiency of 1.2 × 10-4. In the case of large Kr clusters, the best total flux for L-shell X-rays is 5.3 × 1011 photons/J with a conversion efficiency of 1.3 × 10-4 and, for the Kα X-ray (12.7 keV), it is 8 × 10(8) photons/J with a conversion efficiency of 1.6 × 10-6. Using this X-ray source, a single-shot high-performance X-ray imaging is demonstrated.

Interaction of soft x-ray laser radiation with material and caused modification of the exposed surface has both physical and practical interests. We irradiated the focusing soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm and the duration of 7 ps to aluminum (Al) surface. After the SXRL irradiation process, the irradiated Al surface was observed with a scanning electron microscope. The surface modifications caused by SXRL single pulse exposure were clearly seen. In addition, it was found that the conical structures having around 100 nm in diameters were formed in the shallow features. The nano-meter size modified structures at Al surface induced by SXRL pulse is interesting as the newly surface structure. Hence, the SXRL beam would be a candidate for a tool of micromachining. We also provide a thermomechanical modeling of SXRL interaction with Al briefly to explain the surface modification.

The imaging spectrograph with spherical crystal and transmission grating have been used to obtain the high spectrally and spatially resolved images of plasma X-ray microsources (fast z-pinch) as well as of laser-produced plasma flares up to 5 mm in extent. The spectral resolution λ/Δλ = 2·104 have been achieved using a quartz spherical mirror with the curvature radius 500 mm. Using a transmission grating spectrometer, the spectral density of power about 105 W/A in the “water window” has been measured in experiments with a fast z-pinch large pulse storage facility.

Spectroscopic study of plasma produced through bombardment of the 1 × 3 mm2 area on the surface of a solid Mg target with Kr+ ions is carried out. Spectral lines of Mg I and Mg II ions were observed in the visible range (200–600 nm). The plasma parameters Ne = 1.4.1017 cm−3 and Te = 0.8 eV are calculated from electron impact broadening of the 4f–3d line of Mg II and from the ratio of intensities for the 4f–3d and 4s–3p lines of Mg II. The ionic composition of the plasma is determined. The detected X-ray emission is shown to be the characteristic emission of the target.

A short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron–ion equilibrium and increases pressure in a heated layer. The case where the pulse duration τ L is shorter than acoustic relaxation time t s is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless of wavelength. While the physics of electron–ion relaxation strongly depends on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse.

New approaches of a spectrally tunable backlighting schemes based on a spherically bent crystal are considered. In a contrary to the traditional backlighting scheme, in which the investigated objects should be placed between the backlighter and the crystal, for the considered schemes an object is placed downstream of the crystal, before the tangential or after the sagittal focus and an image of the object is recorded at the distance from the object corresponded to the needed magnification. The magnification is defined by the ratio of the distances form the sagittal focus to the detector and from the object to the sagittal focus. A ray tracing modeling and experimental images of test meshes, obtained at an incidence angles of the backlighter radiation of 10° and 22°, are presented. It is demonstrated that, at incident angles up to 22°, a linear transformation of the obtained astigmatic images allows to reconstruct them with an accuracy (5 - 15%). A spatial resolution around 10 μm in a field of view of some mm2 is achieved, for the spectral range around 9 a. It is also demonstrated that spherically bent crystals could be used for X-ray imaging of a self emitting plasma structures with a spatial resolution at least 50 μm in a field of view of some square millimeters for angles of incidence up to 22°.

High resolution x-ray emission spectra of plasma created by laser irradiation of rare-gas (Ar, Kr, Xe) clusters have been measured at laser intensities over 10 19 W/cm 2 and 30-fs pulse duration. To make these measurements possible, in addition to the effort to decrease a prepulse intensity using Pockels cell switches, micron-size clusters were produced using a specially designed conical nozzle. The Boltzmann equation and a detailed collisional radiative model are solved simultaneously as a function of time to model the time integrated x-ray spectra of the transient plasma. The results are quantitatively in good agreement with the experimentally observed x-ray emission spectra of Ar clusters.